The present invention relates to a method for depositing polysilicon on TiO.sub.2.
TiO.sub.2 has highly desirable properties as an electronic material, particularly its large dielectric constant. The dielectric constant of crystalline rutile is approximately 125, and as -deposited polycrystalline TiO.sub.2 can reliably be formed with a dielectric constant of 100 or better. Moreover, polycrystalline TiO.sub.2 has high resistivity, which (for polycrystalline material) can be 10.sup.8 ohm-cm or better.
Thus, it would be highly desirable to be able to use TiO.sub.2 for compact capacitors in integrated circuits. For example, a capacitor one mil square, having a TiO.sub.2 dielectric 100 nm thick atop a 10 nm SiO.sub.2 layer, would theoretically have a capacitance of 2.2 pF. The advantages of such capacitors are particularly desirable in communications and signal processing IC's.
In addition, TiO.sub.2 has the very desirable property that, when applied over a very thin silicon dioxide gate dielectric, the TiO.sub.2 tends to "plug" pinhole defects in the oxide, so that the yield rate on, e.g., 10 nm gate dielectrics is greatly increased. Since the dielectric constant of TiO.sub.2 is so much larger than that of SiO.sub.2, TiO.sub.2 is electrically invisible, and the completed device behaves as if it had only a perfect 10 nm oxide in place. Thus, use of TiO.sub.2 as an extra layer in MIS gate dielectrics would permit very-high-yield fabrication of gate dielectrics which behaved as if they were very thin (10 nm or less).
For many of these applications, it is necessary or highly desirable to deposit polysilicon on TiO.sub.2. For example, the advantages of TiO.sub.2 as a gate dielectric are far less attractive if it can only be used with metal gates. However, a difficulty in the prior art has been that, for previously unknown reasons, the quality of polysilicon which is deposited atop TiO.sub.2 is very poor ("hazy poly").
It is thus an object of the present invention to provide a method for reliably depositing good-quality polysilicon atop TiO.sub.2.
It is a further object of the present invention to provide a method for reliably depositing good-quality polysilicon atop TiO.sub.2 without introducing additional layers of material to the device structure being formed.